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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kartashev A. V., Molokeev M. S., Isaenko L. I., Zhurkov S. A., Fokina V. D., Gorev M. V., Flerov I. N.
Заглавие : Heat capacity and structure of Rb2KMeO3F3 (Me: Mo, W) elpasolites
Коллективы : Siberian Branch of the Russian Academy of Sciences [34]; Russian Federation for the Support of Leading Scientific Schools of the Russian Federation [NSh-4645.2010.2]
Место публикации : Solid State Sci.: ELSEVIER SCIENCE BV, 2012. - Vol. 14, Is. 1. - P.166-170. - ISSN 1293-2558, DOI 10.1016/j.solidstatesciences.2011.11.019
Примечания : Cited References: 12. - This study was supported by the Siberian Branch of the Russian Academy of Sciences (Grant no. 34) and the Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation (NSh-4645.2010.2).
Предметные рубрики: T PHASE-DIAGRAM
Rb2KMoO3F3
TRANSITION
Ключевые слова (''Своб.индексиров.''): oxyfluorides--crystal structure--phase transition--calorimetry
Аннотация: X-ray and heat capacity measurements were performed on Rb2KMoO3F3 and Rb2KWO3F3 single crystals. A significant difference in the thermal parameters of atoms in 4a and 8c sites of Fm-3m structure was found, which depended on the central atom. Calorimetric measurements have revealed the heat capacity anomalies at 195 and 67 K, respectively, in Rb2KMoO3F3 and Rb2KWO3F3. The standard molar enthalpy and entropy were determined. Entropy changes associated with phase transitions in oxyfluorides under study and related Rb2KTiOF5 are discussed. 2011 Elsevier Masson SAS. All rights reserved.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Pogoreltsev E. I., Flerov I. N., Laptash N. M.
Заглавие : Unusual sequence of phase transitions in (NH4)3TiF7 detected by optic and calorimetric studies
Коллективы : Russian Foundation for Basic Research [12-02-00056]; Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation [NSh-924.2014.2]
Место публикации : J. Fluor. Chem.: Elsevier Science, 2014. - Vol. 165. - P.14-19. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2014.05.016. - ISSN 1873-3328
Примечания : Cited References: 13. - This work was supported by Russian Foundation for Basic Research (Grant no. 12-02-00056), and the Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation (Grant no. NSh-924.2014.2).
Предметные рубрики: CRYSTAL-STRUCTURE
DIFFRACTION
NH4F
Ключевые слова (''Своб.индексиров.''): cubic fluorides--phase transitions--crystal-optic--calorimetry
Аннотация: For the first time structural transformations were observed for one of the compounds belonging to the family of double salt fluorides A3MeF7 = A2MeF6·AF. Single crystals of (NH4)3TiF7 = (NH4)2TiF6·NH4F were grown by evaporation of the aqueous solution. Polarizing optical observations, heat capacity and birefringence Δn = (no − ne) measurements were performed in a wide temperature range 100–400 K. Two reversible, first order structural phase transitions were found to be followed by an unusual sequence of symmetry changes: cubic (G3) (T2↓ = 287.5 K; T2↑ = 291–310 K) ↔ P4/mnc (G2) (T1↓ = 358.5 K; T1↑ = 360 K) ↔ 4/m (G1). The twin structures observed were described assuming the existence of cubic parent phase G0 with P m 3 ¯ m symmetry.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Melnikova S. V., Shabanova L. A., Zaitsev A. I., Parshikov S. A., Ageev O. A., Aleksandrov K. S.
Заглавие : Ferroelastic phase transition in Cs3Bi2I9 crystal
Место публикации : Ferroelectrics, Letters Section. - 1996. - Vol. 20, Is. 5-6. - P.163-167. - ISSN 0731-5171
Ключевые слова (''Своб.индексиров.''): birefringence--cesium compounds--crystal symmetry--crystals--differential scanning calorimetry--elasticity--ferroelectricity--permittivity--stiffness--twinning--cesium bismuth iodide--elastic constant--elastic stiffness--ferroelastic phase transition--phase transitions
Аннотация: Phase transition (PT) was found in Cs3Bi2I9 single crystal at T0=223 K. Optical birefringence, dielectric and elastic constants and differential scanning calorimetry have been studied. It was found that birefringence ?nc and twinning picture appeared on (001) - and (100) - plates below T0, as well as softening of elastic stiffness C44 above T0. It allows to classify the PT as proper ferroelastic one with symmetry change 6/mmm - 2/m. В© 1996 OPA (Overseas Publishers Association) Amsterdam B.V. Published in The Netherlands under license by Gordon and Breach Science Publishers SA.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrov K. S., Melnikova S. V., Flerov I. N., Vasiliev A. D., Kruglik A. I., Kokov I. T.
Заглавие : Phase transitions in Cs2CdI4 single crystals
Место публикации : Phys. Status Solidi A. - 1988. - Vol. 105, Is. 2. - P.441-446. - ISSN 0031-8965
Ключевые слова (''Своб.индексиров.''): calorimetry--crystals - structure--dielectric properties--optical properties--x-ray analysis--birefringence--cesium cadmium iodide--dielectric permeability--specific heat--symmetry--cesium compounds
Аннотация: Cs//2CdI//4 crystals were grown from the melt (A) and from water solution (B). Optic, dielectric, X-ray, and calorimetric investigations were carried out. Crystal A shows three phase transitions at 332. 3, 259. 6, and 183. 4 K with the following sequence of phases: commensurate orthorhombic of beta -K//2SO//4 type ( alpha //0 equals 1. 074, b//0 equals 0. 8458, c equals 1. 4852 nm) B ARR LR incommensurate B ARR LR monoclinic ferroelastic (P2//1/n) B ARR LR triclinic ferroelastic (P1 OVER BAR ). The B-crystal belongs to monoclinic symmetry (P2//1/m) and undergoes transformation into the orthorhombic phase of beta -K//2SO//4 type at 420 K.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aleksandrov K. S., Blat D. H., Zinenko V. I., Iskornev I. M., Kruglik A. I., Flerov I. N.
Заглавие : Investigation of ferroelectric phase transitions in CsLiMoO//4 type crystals
Коллективы : European Meeting on Ferroelectricity
Место публикации : European Meeting on Ferroelectricity (5 ; 1983 ; Sept. ; 26-30 ; Malaga, Sp). Ferroelectrics. - 1983. - Vol. 54, Is. 1. - P.573-576. - ISSN 0015-0193
Ключевые слова (''Своб.индексиров.''): calorimetry--cesium compounds - x-ray analysis--phase transitions--ferroelectric materials
Аннотация: X-ray and calorimetric investigations of successive phase transitions (PTs) in crystals of CsLiMoO//4 type were made. The theoretical model description of these PTs as of order-disorder type ones is suggested and thermodynamical properties of the model are discussed.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pogoreltsev E. I., Flerov I. N., Kartashev A. V., Bogdanov E. V., Laptash N. M.
Заглавие : Heat capacity, entropy, dielectric properties and T–p phase diagram of (NH4)3TiF7
Коллективы : Russian Foundation for Basic Research [15-02-02009]; Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation [NSh-924.2014.2]
Место публикации : J. Fluor. Chem.: Elsevier Science, 2014. - Vol. 168. - P.247-250. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2014.10.016. - ISSN 1873-3328
Примечания : Cited References: 16. - This work was supported by the Russian Foundation for Basic Research (Grant no. 15-02-02009), and the Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation (Grant no. NSh-924.2014.2).
Предметные рубрики: CRYSTAL-STRUCTURE
TRANSITIONS
FLUORIDES
NH4F
Ключевые слова (''Своб.индексиров.''): cubic fluorides--phase transitions--dielectric--phase diagram--calorimetry
Аннотация: Successive phase transitions G1 -- G2 -- G3 in the double salt (NH4)(3)TiF7 have been studied by detailed calorimetric, DTA under hydrostatic pressure and dielectric measurements. Rather large entropy jumps at phase transition points were found to be followed by large additional contributions associated with the temperature dependence of the excess heat capacity. The permittivity behaviour and the tangent of the dielectric losses proved the nonferroelectric nature of both transformations. Two triple-points were found on the temperature-pressure phase diagram, suggesting the existence of a hypothetical parent G0 = Pm-3m cubic phase. A direct transformation between high (G0) and low (G3) temperature cubic phases takes place at p 0.41 GPa with a baric coefficient dT(G0) -- (G3)/dp = -40 K/GPa. (C) 2014 Elsevier B.V. All rights reserved.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Melnikova S. V., Vasiliev A. D., Grankina V. A., Voronov V. N., Aleksandrov K. S.
Заглавие : Optical and X-ray studies of mixed crystals CsxRb1-xLiSO4
Коллективы : Russian-Japanese symposium on ferroelectricity
Место публикации : Ferroelectrics: Proceedings of the 1994 5th Russian-Japanese Symposium on Ferroelectricity. Part 2 (of 2) (22 August 1994 through 27 August 1994, Moscow, Russia. - 1995. - Vol. 170, Is. 1. - P.139-143. - ISSN 0015-0193
Ключевые слова (''Своб.индексиров.''): birefringence--cesium compounds--differential scanning calorimetry--phase diagrams--phase transitions--polarization--single crystals--solid solutions--thermal effects--twinning--x ray analysis--mixed crystals--ferroelectric materials
Аннотация: (T-x) phase diagram has been investigated by polarizing optic and birefringence methods, differential scanning calorimetry and X-ray study. A small amount of rubidium in CsLiSO4 as well as cesium in RbLiSO4 reduces the temperature of transition into ferroelastic phase P1121/n which disappear for x?0.15 and x?0.9. The region of phase P21/c11 (c = 2c0) expands and becomes the most stable below ambient temperature for 0.9>x>0.2.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Molokeev M. S., Laptash N. M., Udovenko A. A., Pogoreltsev E. I., Mel'nikova S. V., Misyul S. V.
Заглавие : Structural transformation between two cubic phases of (NH4)3SnF7
Место публикации : J. Fluor. Chem.: Elsevier, 2015. - Vol. 178. - P.86-92. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2015.06.024
Примечания : Cited References: 19. - We thank T.A. Kaidalova for the idea of doubling the unit cell parameter of (NH4)3SnF7 at room temperature. The reported study was partially supported by RFBR, research project No. 15-02-02009 a.
Предметные рубрики: CRYSTAL-STRUCTURE
TRANSITION
NH4F
Ключевые слова (''Своб.индексиров.''): cubic fluorides--phase transitions--x-ray--calorimetry--crystal optics
Аннотация: Reinvestigations of the room temperature structure of ammonium heptafluorostannate (NH4)3SnF7 = (NH4)2SnF6·NH4F = (NH4)3[SnF6]F by both powder and single crystal X-ray diffractions have revealed that its real symmetry is Pa−3 (Z = 8) instead of Pm−3m (Z = 1) suggested earlier. Polarizing optical observations, heat capacity, X-ray powder, and single crystal measurements were performed in a wide temperature range (100–420 K). A reversible structural phase transition of the first order between two cubic modifications Pa−3 ↔ Pm−3m was found at about T0 = 360 K. The structural models associated with partially disordered and totally ordered high and low temperature phases, respectively, comply with a large value of phase transition entropy.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Удод, Любовь Викторовна, Ситников, Максим Николаевич
Заглавие : Влияние катионного замещения на полиморфные переходы в пирасаннате висмута Bi2Sn2O7
Место публикации : Вестник СибГАУ. - Красноярск: СибГАУ, 2015. - Т. 16, № 4. - С. 975-982. - ISSN 1816-9724
Примечания : Библиогр.: 53. - Работа выполнена при финансовой поддержке Российского фонда фундаментальных исследований, грант № 15-42-04099 р_сибирь_а, и государственного задания № 114090470016
Ключевые слова (''Своб.индексиров.''): полиморфные переходы--диэлектрическая проницаемость--электросопротивление--катионное замещение--дифференциальная сканирующая калориметрия--polymorphic transitions--dielectric permeability--cation substitution--electrical resistivity--differential scanning calorimetry
Аннотация: Рассмотрена разработка технологии новых сенсорных материалов, необходимых для газочувствительных приборов, применяемых в ракетостроении. Целью данной работы является изучение влияния допирования разновалентными катионами на кристаллографическую структуру, диэлектрические и электрические свойства пирохлорного соединения Bi 2Sn 2O 7, обладающего селективной избирательностью к газам. Методом твердофазного синтеза впервые синтезированы соединения Bi2(Sn1-xMex)2O7, где Me = Mn, Cr, x = 0, 0,05, находящиеся сразу в двух полиморфных модификациях - орторомбической и кубической. В твердых растворах Bi2(Sn0,95Cr0,05)2O 7 методом сканирующей калориметрии обнаружено два новых структурных перехода, по сравнению со станнатом висмута Bi2Sn2O7. Ионы Mn 4+ сместили фазовые границы полиморфных переходов в сторону меньших температур, а фазовый α→β-переход около 370 К, характерный для Bi2(Sn1-xCrx)2O7, где x = 0, 0,05, подавили почти полностью. Полиморфный переход при Т = 543 К для Bi 2(Sn0,95Mn0,05) 2O 7 протекает с выделением тепла, в отличие от Bi2(Sn1-xCrx)2O7, где x = 0, 0,05. Исследована взаимосвязь структурных, электрических и диэлектрических свойств. Установлены аномалии в температурной зависимости электросопротивления и диэлектрической проницаемости (мнимой и реальной частями) как в области низких температур, так и при высоких температурах. Эти особенности объясняются в рамках модели мартенситных фазовых переходов. Методом сканирующей калориметрии найдены температуры структурных фазовых переходов, которые коррелируют с аномалиями электросопротивления в интервале температур 300 T 1000 К для Bi2(Sn1-xCrx)2O7, x The goal of this work is to develop a new technology of sensor materials required for gas sensing devices used in missile. The aim of this work is to study the effect of doping cations with different valency on the crystallographic structure, dielectric and electrical properties of pyrochlore compound Bi2Sn2O7 with selectivity to gases. Polycrystalline compounds Bi2(Sn1-xMex)2O7, where Me = Mn, Cr, x = 0, 0.05 have been synthesized by conventional solid-state reaction. According to the X-ray powder diffraction research, our sample consists of two polymorphs phases: cubic and rhombic. Two new structural transition are found in Bi2(Sn0.95Cr0.05)2O7 solid solutions by scanning calorimetry, as compared to bismuth pyrostannate Bi2Sn2O7. Ions Mn 4+ leads to shift of phase boundary of polymorphic transitions towards lower temperatures, and the phase α→β-transition at about 370 K, which is characteristic for Bi2(Sn1-xCrx)2O7, where x = 0, 0.05 is suppressed. The polymorphic transition at T = 543 K for Bi2(Sn0.95Mn0.05)2O7 occurs with calorification, in contrast to Bi2(Sn1-xCrx)2 7, where x = 0, 0.05. The relationship between structural, electrical and dielectric properties is investigated. Anomalies in the temperature dependence of electrical resistivity and dielectric permeability (real and imaginary part) as in the low region temperatures as in the high region temperature are found. These features are explained within a model of martensitic phase transitions. The temperature of the structural phase transitions correlates with temperature of maximum of the electrical resistivity in the temperature range 300 T 1000 K for Bi2(Sn1-xCrx)2O7, x
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Morozov E. V., Martyanov O. N.
Заглавие : Probing flocculant-induced asphaltene precipitation via NMR imaging: from model toluene-asphaltene systems to natural crude oils
Коллективы : Russian Science Foundation [15-19-00119]
Место публикации : Appl. Magn. Reson.: Springer, 2016. - Vol. 47, Is. 2. - P.223-235. - ISSN 0937-9347, DOI 10.1007/s00723-015-0741-9. - ISSN 1613-7507(eISSN)
Примечания : Cited References:46. - This research was performed with the financial support of Russian Science Foundation (project no. 15-19-00119).
Предметные рубрики: PETROLEUM ASPHALTENES
MOLECULAR-DYNAMICS
AGGREGATION
MICROSCOPY
SCATTERING
RESONANCE
SEDIMENTATION
ASSOCIATION
CALORIMETRY
RELAXATION
Аннотация: An nuclear magnetic resonance (NMR) imaging approach for studying flocculant-induced asphaltene precipitation processes is introduced in this report. Unlike commonly accepted techniques, which primarily measure aggregation processes on the submicron scale (the level of asphaltene molecules and their aggregates), NMR imaging demonstrates the capability to obtain new useful information about bulk system behavior on the macro scale. To reveal the capabilities of the method, the model toluene-asphaltene system and two samples of natural crude oils with different chemical composition and physical properties (such as asphaltene content and density) were employed for experiments. The process of colloidal suspension formation and two different patterns of its evolution were observed depending on both the asphaltene content and the flocculant concentration. In the first pattern, the flocculant-induced precipitation leads to the slow uniform compacting of the suspension and descent of the sedimentation front, whereas the second pattern is characterized by sediment accumulation and the upwards drift of the front. It was found that the behavior of the precipitated asphaltenes in the model system correlates well with those observed in natural crude oils. The results achieved in this work are in agreement with the data obtained previously via other techniques. Thus, NMR imaging proved to be an efficient method for probing flocculant-induced precipitation in crude oils.
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